Flame tube



NOV 20, 1962 J. G. ToMLlNsoN' 3,064,424

' FLAME TUBE: Filed sept. 5o, 1959 2 sheets-sheet 1 /4/ f//f a? u IN VENT 0R.

/ ATTORNEY Bli-,ii Patented Nov. 29, i962 3,064,424 Finali/E TUBE Jerry G. Tomlinson, Speedway, Ind., assigner to General Motors Corpcratien, Retrait, Mich., a corperation of Delaware Filed Sept. 3?, 1959, .3era-N0. 843,555 13 Ciaims. (PCi. oil-39.65)

My invention is directed to combustion apparatus, and particularly to such as is used in gas turbine engines. Combustion devices of this sort are characterized by very high energy release for unit volume and time, and thus have presented difficult problems in the achievement of satisfactory combustion. It is generally believed that a rapid and intimate mixture of finely sprayed fuel and combustion air and some turbulence and recirculation of the combustion air and combustion products are essential to burning fuel at a high rate in the small combustion space ofthe usual gas turbine engine.

Prior efforts have succeeded in developing combustion apparatus which are, in general, very satisfactory, in which combustion is relatively stable, and in'which the life of theV combustion liner or flame tube within which burning is eected is satisfactory.

However, eorts to obtain even temperature distribution of the combustion products delivered and to achieve compiete burning and freedom from smoke in the combastion products have not been fully successful. My invention is directed particularly to improvements in the forward, upstream, or inlet end of flame tubes, which `may otherwise be in accordance with the best known practices in the art, so as to improve the temperature distribution and eliminate smoky combustion, and retain or improve stability of combustion under various conditions of air pressure and fuel rate.

The nature of the invention, and the advantages there- Vof, will be apparent to those skilled in the art from the succeeding detail description of the preferred embodiment of the invention and the accompanying drawings thereof.

FIGURE l is a partial View of an axial flow gas turbine engine taken on a plane containing the axis of the engine.

FGURE 2 is a view, with parts cut away and in section, of the forward portion of a llame tube.

FGURE 3 is an enlarged View of thev forward portion of the combustion apparatus, taken on the same plane as .FfGURE l, and illustrating air flow within the flame tube.

FIGURE 4 is a front elevational View of the flame tube vtaken on the plane indicated by the line 4 4 in FIG- URE 2.

Referring first to FIGURE l for a description of the preferred environment of the invention, the ame tube vthe space id, from which it fiows through apertures to be described into a number of substantially parallel fiame tubes iii distributed around the axis of the engine. Each `flame tube has at its rear end a transition section i7 which varies in section from circular at the forward end to a sector ofV an annulus at its rearward end. The rear end `of the transition section is mounted inthe turbine case 13 and discharges into the nozzle 1S of a turbine, the r..-

.mainder of which is not illustrated. The turbine drives the compressor, which supplies air to the combustion apparatus in which fuel is'burned. The resulting combustion products are the motive fluid of the turbine. The fuel is admitted to each, flame tube or liner 10 by a fuel nozzle 19, which includes a mounting plate 21 fixed to the diffuser structure 11.

In addition to the transition section i7, each liner includes a generally cylindrical body 22, composed of a number of sections welded together, and a dome 23 at the forward end of the body. Referring to FiGURE 3, an igniter 24 suitably mounted on the engine projects through `a ferrule Zxed in the body22. Two conruectionsZI are ing engagement of the transition section 17' on the turbine nozzle and at the forward end by a piloting engagement of the dome on the tip 29 of the fuel nozzle. lt is located axially by the igniter plug 24 or equivalent locating means. Y

The dome 23 is of hemi-toroidal shape, being a surface of revolution including a marginal flange 3G, a conical portion 31 and a curved rearwardly-directed central portion 32. An inlet air swirler 33 is fixed in the portion 2 of the dome. The swirler comprises an outer annular wall portion orring 3,4, an inner ring A35, and a number of helical vanes 36 extending between the inner and outer rings. Thepassages between the vanes converge rearwardly so that the air discharged from the outlet 37 between the vanes flows at high velocity. The vanes preferably are pitched at an angle of about 60 to the axial direction to impart a strong tangential or swirl velocity to the air. The forward inner portion of the ring 34 and of the vanes 35l defines a conical funnel which facilitates mounting the llame tube over the nozzle tip 29 -when the engine is assembled.

Proceeding with the preferred structural details of the body portion 22 of the flame tube, this comprises `a series of slightly coned rings 38, 39, 41, and 42 and the cylindrical section 43. These are aligned coaxially with the forward end of each approximately in the same plane as therearward end of the one just ahead of it, and are connected by corrugated strips 5.5, the inward corrugations of which are spot-welded to the forward adjacent ring and the outer corrugations of which are spot-welded to the rearward adjacent ring. Notches 4a in the rearward edges of the rings eliminate stresses due to differential expansion which might otherwise cause undue distortion or cracking. of the liner. The spaces left by the corrugated rings 45 between the adjacent liner sections admit film cooling air which flows along the inner surface of the liner, providing a considerable degree of cooling.

An air-cooled stiffening ring 47 is fixed to the rear end of the section 43, and an air-cooled reinforcing structure 4S is fixed to the outer rear surface of the transition section 37. These structures and, in general, the portion of the liner from section 432 to the discharge eno thereof may be the same or substantially the same as that described in application Serial No. 699,784 filed November 29, 1957, now abandoned, of common ownership with this application. (This application is abandoned, but reference may be made to British Patent No. 851,125 or Canadian Patent No. 635,106).

The dome 23 is fixed to the forward body section 3S by a corrugated strip or ring 56 which extends around the inside of the circumference of both the dome and the body. The strip 5G has flat, shallow corrugations extending axially of the liner. There is a gap indicated at Si between the dome and the remainder of the liner which is bridged by the strip-S0. The outward corrugations of the strip are spot-welded to the dome Z3 and to section 3S. Air entering through the gap 51 flows forwardly and rearwardly as indicated in the upper portion of FlG- URE 3, through the spaces defined by the inward corrugations of the strip 50. A hole 52 is provided in each outward corrugation of the strip 50 for admission of air. The holes S2 are underlaid by a segmented ring 54 spotwelded to the ring or strip 50. The segmented ring 54 is provided by spot-welding a continuous ring to the strip 50 and then slotting the ring as indicated at 5S beneath each outward corrugation of strip 5G. The slotting or dividing of ring 54 eliminates thermal stresses. The slots are quite narrow, but provide for relative expansion or contraction of ring 54 and the strip 50. The ring 54 deects the air entering through the openings 52 so that substantially all of it also flows in both forward and rearward directions, as indicated in the lower portion of FIGURE 3. It will be Seen, therefore, that the air admitted through the gap between the dome and the liner is divided into two portions, each of which provides a substantially continuous iilm or sheet of air, one sheet moving rearwardly to provide film cooling of the section 3S of the liner, and the other portion flowing forwardly and then being deflected inwardly and rearwardly by the dome, as indicated by the arrows in FiGURE 3.

The air thus deflected rearwardly by the dome mixes with and is energized by the high velocity swirling air entering through the swirler outlet 37 which, because of its swirling motion, tends to move radially outwardly as well as rearwardly. The mixing of the swirling and nonswirling streams of air results in considerable highly desirable turbulence and provides a cone of turbulent air moving into the cone of the fuel spray indicated by the broken lines 57 in FIGURE 3. This turbulent air mixes rapidly with the fuel spray and provides favorable conditions for initiation of combustion.

Additional air is supplied to the primary zone of combustion through relatively small holes in the first three sections 3S, 39, and 41 of the liner. Two diametrically opposite holes 58 are provided in section 38, three approximately equally spaced holes 59 are provided in section 39, and four approximately equally spaced holes 61 are provided in section 41. These holes provide primary or combustion air. The air entering through these holes is admitted in a generally radial direction and the air admitted through holes 58 and 59 tends to veer forwardly towards the fuel nozzle because of a vortex ring created by the outward ow of the fuel and of the air flowing from the dome and swirler. The result is a vortex ring in the area indicated by 62 in which air heated by combustion, combustion products, and partially burned fuel are thoroughly and evenly mixed, with symmetrical combustion about the axis of the liner.

The film cooling air serves primarily for liner cooling and then dilution of the combustion products, although it is possible for it to enter the combustion to some extent. A relatively large portion of the air, which serves entirely as dilution air, is admitted through six large holes 63 in the section 43 of the liner. Further mixing of this dilution air and combustion products occurs during its flow rearwardly to the turbine nozzle.

bustion space wall to provide a loose temporary attachment of the liner prior to its engagement with the nozzle during assembly of the engine.

It has been found by test that a combustion liner of the configuration shown in the drawings and described gives exceptionally uniform temperature distribution at the outlet and is free from smoking or incomplete combustion under all normal operating conditions. These beneficial results arise from the improved configuration of the forward end of the liner, since prior liners with which 1t has been compared are substantially identical except for the arrangement of the parts forward of the location of the crossover tubes.

It will be helpful in understanding the operation of my improved liner to set out the presently preferred proportions of air iiow through the various openings or entrances to the liner. lt will be understood, however, that these proportions are variable to suit specific conditions, such as pressure ratio of the engine and so forth. In the preferred liner configured to suit a known turbo-prop engine, the distribution is as follows. Considering the proportion of compressor discharge air which is admitted to one combustion liner as the swirler admits 4.6% and the forwardly owing portion of the air admitted through the gap 51 is 7.8%.

Section 3S admits 1.5% through holes 58 and section 39 admits 5.3%, mostly through holes 59, although a small amount enters through the holes 67. Section 41 admits 7.2% through the four holes 51. This is a total of about 26%, which is sucient air to complete combustion, and all this air may be regarded as the primary or combustion air.

It will be seen that most of the combustion air enters into the vortex ring in the area into which the fuel is injected.

lt may be also noted that experiments with the liner structure of the invention indicate that the hemi-toroidal or recurved form of the dome with the flow of air inwardly over the dome is the significant factor in the elimination of smoke from the combustion process. However, the admission of the rapidly swirling air through the inlet swirler improves the stability of combustion, and therefore benefits the overall operation when employed with the toroidal dome.

The film cooling air, including the rearwardly flowing air admitted through gap 51 and the air admitted through the four additional joints between the sections of the liner admits to 39.1%. The remaining 34.5 is dilution air, admitted principally through the six holes 63, although a small amount enters through the air-cooled reinforcing members 47 and 48.

It will be apparent that the structure described, in addition to its important advantages from the standpoint of improved combustion, is also a structure minimizing thermal stresses in the parts of the liner and providing good cooling of the wall of the liner.

The description of the preferred embodiment of the invention, for the purpose of explaining the principles thereof, is not to be construed as limiting the scope of the invention, since many modifications may be made by the exercise of skill in the art.

I claim: o

tl. A iiame tube for a combustion apparatus of a ga turbine or the like, the ame tube comprising, in combination, a generally cylindrical body having a forward end and a rearward outlet end, an imperforate hernitoroidal dome substantially closing the forward end, an air swirler converging in the rearward direction mounted in the center of the dome providing a central opening to receive a fuel spray nozzle, the margins of the dome and body being spaced to define between them a forwardly directed air entrance configured to admit air forwardly of the ame tube, the forwardly admitted air owing over the inner surface of the dome and being directed rearwardly thereby and mixing with the air admitted through the swirler adjacent the fuel nozzle, the flame tube being provided with further openings downstream of those recited for admission of additional combustion air and dilution air.

2. A flame tube for a combustion apparatus of a gas turbine or the like, the flame tube comprising, in combination, a generally cylindrical body having a forward end and a rearward outlet end, an imperforate hernitoroidal dome substantially closing the forward end, an air swirler mounted in the center of the dome exteriorly of the llame tube providing a central opening to receive a fuel spray nozzle, a corrugated strip having corrugations directed axially of the flame tubexed to and within the dome and the body, the Ystrip extending Yaround Ythe circumference ofthe dome and-body, the margins of the dome and body being spaced to define air entries cooperating with the inward corrugations of the strip to admit air forwardly andrearwardly of the flame tube, the forwardly admitted air flowing over the inner surface of the dome and being directed rearwardly thereby and mixing with the air admitted through the swirler adiacent the fuel nozzle, the flame tube being provided with further openings downstream of those recited for admission of additional combustion air and dilution air.

3. A flame tube for a combustion apparatus of a gas turbine or the like, the flame-tube comprising, in combination, agenerally cylindrical body having a forward end and a rearward outlet end, an imperforate hemitoroidal dome substantially closing the forward end, an air swirler mounted in the center of the dome providing a central opening to receive a fuel spray nozzle, a corrugated strip having corrugations directed axially of the name tube fixed to and within the dome and the body, the strip extending around the circumference ofthe dome and body, the margins of the dome and body being spaced to define air entries cooperating with the inward corrugations of the stripto admit air'forwardly and rearwardly of the llame tube, a ftat ring fixed to and within the corrugated stripand substantially bridging the gap between the dome andV body, the corrugated strip having apertures in the outward corrugations thereof cooperating with the ring to admit air forwardly and rearwardly of the flame tube, the forwardlyl admitted air flowing over the inner surface of' the dome and being directed rearwardly thereby and mixing with the air admitted through the swirler adjacent the fuel nozzle, the flame tube being provided with further openings downstream of those recited for admission of additional combustion air and dilution air. l

4. A flame tube for a combustion apparatus of a gas turbine or the like, the flame tube comprising, in cornbination, a generally cylindrical body having a forward end and a rearward outlet end, an imperforate hemitoroidal dome substantially closing the forward end, an air swirler converging in the rearward direction mounted in the center of the dome exteriorly of the llame tube and providing a central opening to receive a fuel spray nozzle, a corrugated strip having corrugations directed axially of the flame tube fixed to and within the dome and the body, the strip extending around the circumference of the dome and body7 the margins of the dome and body being spaced to define air entries cooperating with the inward corrugations of the strip to admit air forwardly and rearwardly of the llame tube, a flat segmented ring fixed to and within the corrugated strip and substantially bridging the gap between the dome and body, the corrugated strip having apertures in the outward corrugations thereof cooperating with the ring to admit air forwardly and rearwardly of the llame tube, the forwardly admitted air flowing over the inner surface of the dome and being directed rearwardly thereby and mixing with the air admitted through the swirler adjacent the fuel nozzle, the llame tube being provided with further openings downstream of those recited for admission of additional combustion air adjacent the dome for admixture with the air admitted through the swirler aud forwardly at the margin of the dome.

5. A flame tube for a combustion apparatus of a gas turbine or the like, the flame tube comprising, in combination, a generally cylindrical body having a forward end and a rearward outlet end, an imperforate hemi-toroidal dome substantially closing the forward end and providing a central opening to receive a fuel spray nozzle, a corrugated strip having corrugations directed axially of the flame tube fixed to and within the dome and the body, the strip extending around the circumference of the dome and body, the margins of the dome and. body Ibeing spaced to define air entries cooperating with the inward corrugations of the stripto admit air forwardly andrearwardly of the flame tube, the forwardly admitted air flowing over the inner surface of the dome-and being directed rearwardly thereby adjacent the fuel nozzle, the flame tube being provided with further openings downstream of-those recited for admission of additional combustion air and dilution air.

6. A flame tube for a combustion apparatus of a gas turbine or the like, the flame tube comprising, in combination, a generally cylindrical body having a forward end and a rearward outlet end, an imperforate hemi-toroidal dome substantially closing the forward end and providing a central opening to receive a fuel spray nozzle, a corrugated strip having corrugations directed axially of the llame tube fixed to and within the dome and the body, the strip extending around the circumference of the dome and body, the margins of the dome and body being spaced to define air entries cooperating with the inward corrugations of the strip to admit air forwardly and rearwardly of the flame tube, a flat ring fixed to andrwithin the corrugated strip and substantially bridging the gap between the dome and tbody, the corrugated strip having apertures in the outward corrugations hereof cooperating with the ring to admit air forwardly and rearwardly of the flame tube, theforwardly admitted air flowing over the inner surface'of-the Vdome and being directed rearwardly thereby adjacent the fuel nozzle, the flame tube being provided-with further openings downstream of those recited for admission of additional combustion air and dilution air.

7. A llame tube for a combustion apparatusof aY gas turbine or the like having an upstream end portion including a body portion and a hemi-toroidal imperforate dome fixed to the forward end of the body portion bulging forwardly and terminating in a central rearwardlydirected portion, an air swirler mounted in the said rearwardly-directed portion defining a pilot for a fuel nozzle adapted to locate the spray tip of the nozzle centrally of the rearward end of the swirler, means at the outer margin of the dome for admitting a substantially circumferentially continuous sheet of forwardly-flowing air over the rearward face of the dome, the said air being deflected inwardly and rearwardly by the dome and mixing with the air admitted through the swirler to create a turbulent air flow mingling with the fuel spay from the nozzle.

8. A flame tube for a combustion apparatus of a gas turbine or the like having an upstream endportion including a body portion and a heini-foroidal imperforate dome fixed to the forward end of the body portion bulging forwardly and terminating in a central rearwardlydirected portion, an air swirler mounted in the said rearwardly-directed portion exteriorly of the flame tube, the swirler defining rearwardly converging swirl passages and defining a pilot for a fuel nozzle adapted to locate the spray tip of the nozzle centrally of the rearward end of the swirler, means at the outer margin of the dome for admitting a substantially circumferentially continuous sheet of forwardly-flowing air over the rearward face of the dome, the said air being deflected inwardly and rearwardly by the dome and mixing with the air admitted through the swirler to create a turbulent air flow mingling wtih the fuel spray from the nozzle.

9. A flame tube for a combustion apparatus of a gas turbine or the like having an upstream end portion including a body portion and a hemi-toroidal imperforate dome fixed to the forward end of the body portion bulging forwardly and terminating in a central rearwardly-directed portion, an air swirler mounted in the said rearwardlydirected portion exteriorly of the flame tube, the swirler delining rearwardly converging swirl passages and defining a pilot for a fuel nozzle adapted to locate the spray tip of the nozzle centrally of the rearward end of the swirler, means at the outer margin of the dome including a corrugated strip connecting the dome and the body for admitting a substantially circumferentially continuous sheet of forwardly-owing air over the rearward face of the dome, the said air being deected inwardly and rearwardly by the dome and mixing with the air admitted through the swirler to create a turbulent air flow mingling with the fuel spray from the nozzle.

10. A flame tube for a combustion apparatus of a gas turbine or the like having an upstream end portion including a body portion and a hemi-toroidal imperforate dome xed to the forward end of the body portion bulging forwardly and terminating in a central rearwardlydirected portion, an lair swirler mounted in the said rearwardly-directed portion exteriorly of the -iame tube, the swirler defining rearwardly converging swirl passages and defining a pilot for a fuel nozzle adapted to locate the spray tip of the nozzle centrally of the rearward end of the swirler, means at the outer margin of the dome for aldmitting a substantially circumferentially continuous sheet of forwardly-flowing air over the rearward ace of the dome, the said air being deflected inwardly and rearwardly by the dome and mixing with the air admitted through the swirler to create a turbulent vortex ring air ow mingling with the fuel spray from the nozzle, and means providing openings in the body for radially inwardly owing air jets adjacent the fuel spray adapted to commingle with the air in the vortex ring ow.

11. A ame tube for a combustion apparatus of a gas turbine or the like comprising two coaxial sections having walls lying substantially in a common surface, the walls being separated by a gap, a corrugated strip having l corrugations extending across the gap within the sections and directing air entering through the gap axially along the inner surface of both walls, holes in the outward convolui tions of the strip, and a deflector ring xed to the inward convolutions directing the air entering through the holes axially along the inner surface of both Walls.

12. A iame tube for a combustion apparatus of a gas turbine or the like comprising two coaxial sections having walls lying substantially in a common surface, the walls being separated by a gap, a corrugated strip having corrugations extending across the gap within the sections and directing air entering through the gap axially along the inner surface of both walls, holes in the outward convolutions of the strip, and a segmented deector plate ring xed to the inward convolutions directing the air entering thrnugh the holes axially along the inner surface of both wa ls.

13. A ame tube for a combustion apparatus of a gas turbine or the like comprising two coaxial sections having walls lying substantially in a common surface, the walls being separated by a gap, and a corrugated strip connecting the sections having corrugations extending across the gap and extending within the inside of both sections so as to direct air entering through the gap laxially along the inner surface of both walls when a pressure drop into the flame tube causes air to enter through the gap.

References ited in the file of this patent UNITED STATES PATENTS 2,537,033 Christensen Jan. 9, 1951 2,555,965 Garber June 5, 1951 2,603,064 Williams July 15, 1952 2,651,912 Abbott V .Y. Sept. l5, 1953 2,657,531 Pierce -Nov. 3, 1953 2,768,497 Hayes Oct.'30, 1956 FOREIGN PATENTS 1,060,667 Germany July 2, 1959 

